The present invention relates to a control system and method for a multi-cylinder internal combustion engine.
There has been proposed a control system for electronically controlling a throttle valve and thereby controlling a torque of an engine as disclosed in Japanese Patent Provisional Publication No. 11-182298.
In the meantime, for the purpose of attaining an improved fuel consumption, reduced shift shock, etc., it has been developed a multi-cylinder internal combustion engine which can electromagnetically control the operation mode of intake and exhaust valves of each cylinder. Namely, the engine is constructed so as to perform:
(1) switching between a full cylinder operation with all of the cylinders in operation and a part cylinder operation with some of the cylinders kept out of operation; and
(2) switching between a standard cycle operation in which the engine is operated in a standard cycle (e.g., four-stroke cycle) and a modified cycle operation in which the engine is operated in a modified cycle different in the number of cycles from the standard cycle by controlling the operation of the intake and exhaust valves for thereby providing the standard cycle with an additional recompression stroke and an additional re-expansion stroke.
It is found that when a conventional throttle valve control system is applied to such a multi-cylinder engine as it is, there is caused a difference in torque between the times before and after switching to the part cylinder operation or to the modified cycle operation since the throttle valve opening degree is held unchanged before and after the switching.
In this connection, description is made by taking the engine adapted to perform the above described switching (1) as an example. At the time of switching from the full cylinder operation to the part cylinder operation, the torque cannot be maintained unchanged before and after the switching unless the torque produced by each cylinder at the part cylinder operation is made larger as compared with that at the full cylinder operation. Unless there is a difference in the quantity of intake air flowing through the throttle valve between the times before and after the switching, the quantity of intake air supplied to each operative cylinder at the part cylinder operation is increased naturally so that the torque produced by the engine must be held unchanged before and after the switching. However, in fact, the intake manifold vacuum is decreased with increase of the quantity of intake air per each cylinder at the part cylinder operation. Due to this, the pressure differential across the throttle valve is decreased, thus causing the quantity of air flowing through the throttle valve to decrease. Accordingly, in order that the quantity of intake air flowing through the throttle valve is maintained unchanged before and after the switching, it is necessary after switching to the part cylinder operation to make the opening of the throttle valve larger than that at the full cylinder operation. However, in the conventional control system, consideration on this matter has not yet been made and therefore the throttle valve opening degree is maintained unchanged before and after switching to the part cylinder operation, thus causing a sharp variation of torque at the time of the switching.
It is accordingly an object of the present invention to provide a control system for a multi-cylinder internal combustion engine that can prevent a sharp variation of torque at the time of switching from the full cylinder operation to the part cylinder operation or vice versa, by determining a target intake air quantity per one operative cylinder at the part cylinder operation in consideration of the fact that there is a difference in the influence on the quantity of intake air flowing through the throttle valve between the full cylinder operation and the part cylinder operation.
It is a further object of the present invention to provide a control system for a multi-cylinder internal combustion engine that can prevent a difference in torque between a standard cycle operation and a modified cycle operation, by determining a target intake air quantity per one cylinder at the modified cycle operation in consideration of the fact that then is a difference in the influence on the quantity of intake air flowing through the throttle valve between the standard cycle operation and the modified cycle operation.
It is a further object of the present invention to provide control methods for multi-cylinder internal combustion engines that are executed by the control systems of the foregoing character.
To achieve the above objects, there is provided according to an aspect of the present invention a control system for a multi-cylinder internal combustion engine in which switching between a full cylinder operation with all cylinders in operation and a part cylinder operation with some of cylinders kept out of operation is selectively performed, comprising a first calculator for calculating, at the part cylinder operation, a target air fuel quantity per one operative cylinder that enables the engine to produce a torque equal to that at the full cylinder operation, a second calculator for calculating a throttle valve target opening area at the part cylinder operation from the target intake air quantity per one operative cylinder, and a controller for controlling a throttle valve opening degree so that the throttle valve target opening area is obtained.
According to another aspect of the present invention, there is provided a control system for a multi-cylinder internal combustion engine in which switching between a standard cycle operation in which the engine is operated in a standard cycle and a modified cycle operation in which the engine is operated in a modified cycle different in the number of strokes from the standard cycle by controlling operations of intake and exhaust valves, comprising a first calculator for calculating, at the modified cycle operation, a target intake air quantity per one cylinder that enables the engine to produce a torque equal to that at the standard cycle operation, a second calculator for calculating a throttle valve target opening area at the modified cycle operation from the target intake air quantity per one cylinder, and a controller for controlling a throttle valve opening degree so that the throttle valve target opening area is obtained.
According to a further aspect of the present invention, there is provided a control system for a multi-cylinder internal combustion engine in which switching between full cylinder operation with all cylinders in operation and part cylinder operation with some of cylinders kept out of operation is selectively performed, comprising means for calculating, at the part cylinder operation, a target air fuel quantity per one operative cylinder that enables the engine to produce a torque equal to that at the full cylinder operation, means for calculating a throttle valve target opening area at the part cylinder operation from the target intake air quantity per one operative cylinder, and means for controlling a throttle valve opening degree so that the throttle valve target opening area is obtained.
According to a further aspect of the present invention, there is provided a control system for a multi-cylinder internal combustion in which switching between a standard cycle operation in which the engine is operated in a standard cycle and a modified cycle operation in which the engine is operated in a modified cycle different in the number of strokes from the standard cycle by controlling operations of intake and exhaust valves, comprising means for calculating, at the modified cycle operation, a target intake air quantity per one cylinder that enables the engine to produce a torque equal to that at the standard cycle operation, means for calculating a throttle valve target opening area at the modified cycle operation from the target intake air quantity per one cylinder, and means for controlling a throttle valve opening degree so that the throttle valve target opening area is obtained.
According to a further aspect of the present invention, there is provided a control method for a multi-cylinder internal combustion engine in which switching between full cylinder operation with all cylinders in operation and part cylinder operation with some of cylinders kept out of operation is selectively performed, comprising calculating, at the part cylinder operation, a target air fuel quantity per one operative cylinder that enables the engine to produce a torque equal to that at the full cylinder operation, calculating a throttle valve target opening area at the part cylinder operation from the target intake air quantity per one operative cylinder, and controlling a throttle valve opening degree so that the throttle valve target opening area is obtained.
According to a further aspect of the present invention, there is provided a control method for a multi-cylinder internal combustion engine in which switching between a standard cycle operation in which the engine is operated in a standard cycle and a modified cycle operation in which the engine is operated in a modified cycle different in the number of strokes from the standard cycle by controlling operations of intake and exhaust valves, comprising calculating, at the modified cycle operation, a target intake air quantity per one cylinder that enables the engine to produce a torque equal to that at the standard cycle operation, calculating a throttle valve target opening area at the modified cycle operation from the target intake air quantity per one cylinder, and controlling a throttle valve opening degree so that the throttle valve target opening area is obtained.